This invention relates to a cut pile tufting machine cutting system and more particularly to tufting machine hooks mounted within a hook module at a compound angle to improve cutting and to reduce J-cutting.
In the production of cut pile tufted fabric, each reciprocating needle cooperates with a hook which seizes a loop of yarn from the needle and holds the loop until it is cut by a knife acting in scissors-like fashion against the side of the hook to form the pile. The cutting action occurs as the hook and knife oscillate along different paths. Conventionally, hooks were mounted within a hook bar and the knives mounted within a knife bar. More recently, the hooks are mounted in modular form within a modular body member and the knives likewise may be mounted in such module form. The modules are molded about the shanks of the respective hooks or knives so that each is properly aligned with respective other hooks and knives. Since the knives act against the face of the respective hooks in scissors-like fashion with sufficient pressure, the knife block or the knife module is pivoted on the bar to which it is attached to engage the face of the hook at a compound angle, i.e., an angle of inclination, and an angle of canter. An angle of inclination of 8.degree. and an angle of canter of approximately 4.degree. has been used in the prior art. The combination of the angle of inclination and the angle of canter provides a compound angle between the knives and the respective hooks. Cutting action requires that there be tension or pressure of the knife against the hook in a sufficient amount so as to obtain the scissors-like cutting. The required initial tension or loading of the knife against the hook has required the knife bar or module to be adjusted so that the knife actually flexes or bends due to the loading or force between the knife and the hook. This results in a high force or load on the knife and results in rapid knife wear and also in wear of the cooperating surfaces of the hook.
There are limitations on the loading of the knife against the hook since cutting occurs at a location adjacent to the throat of the hook and if contact occurs between the surface of the knife below the cutting edge and the surface of the hook behind the throat, the knife is said to be "heeling" against the hook and cutting either ceases or very rough cutting occurs. Moreover, the range of tension on the knife is limited in very fine gauge tufting machines since a knife may contact an adjacent hook. In such fine gauge machines, a knife relief may be ground into the surface of the hook remote from the cutting surface to prevent or minimize such interference. Consequently, the required knife tension during cutting is difficult to attain with hooks of the prior art. Moreover, in fine gauge machines, the thickness of the yarns that may be cut may be limited because of the limitations on the tension that can be applied between the knives and the hooks.
Another major problem encountered during cutting in a tufting machine results from the fact that the knives act against one face of the hook, and since the hook has a thickness, the leg of the yarn cut against the cutting surface of the hook is shorter than the other leg by an amount substantially equal to the thickness of the hook. This is known as "J cutting." Thus, the pile fabric produced has unequal lengths projecting from the backing material and requires excessive tip shearing.
In Cox, U.S. Pat. No. 4,602,576, a proposal was made to remedy the aforesaid problems by proposing a hook having an inclined ramp on the face of the hook adjacent to the cutting edge, the ramp being a relief in the surface which acts as a cam surface to direct the knife as the knife oscillates adjacent to the throat of the hook. The cam surface is ground at an angle relative to the blade of the hook to increase the distance between the surface of the knife below the cutting edge and the surface of the hook behind the throat and to permit greater tension to be applied between the knife and the hook without resulting in "heeling" of the knife against the hook. As the flexed knife rides up the cam surface the distance between these surfaces will actually increase resulting in an increase in tension as the cutting edges approach each other. The proposal also was to provide an additional relief on the cutting edge of the hook as a continuation of the cam surface or at a slightly different slope to place the cutting edge substantially between the opposed surfaces of the blade of the hook in an effort to eliminate the "J" cutting problem. However, after unsuccessful attempts were made to develop hooks constructed in accordance with this proposal, efforts were abandoned.